Information About NSEL

The adaptive security appliance supports NetFlow Version 9 services. For more information about NetFlow services, see RFCs.

The adaptive security appliance implementation of NSEL is a stateful, IP flow tracking method that exports only those records that indicate significant events in a flow. In stateful flow tracking, tracked flows go through a series of state changes. NSEL events are used to export data about flow status, and are triggered by the event that caused the state change.

The significant events that are tracked include flow-create, flow-teardown, and flow-denied (excluding those flows that are denied by EtherType ACLs). Each NSEL record has an event ID and an extended event ID field, which describes the flow event.

The adaptive security appliance implementation of NSEL provides the following major functions:

•Defines and exports templates that describe the progression of a flow. Templates describe the format of the data records that are exported through NetFlow. Each event has several record formats or templates associated with it.

•Tracks configured NSEL collectors and delivers templates and data records to these configured NSEL collectors through NetFlow over UDP only.

•Filters NSEL events based on the traffic and event type through Modular Policy Framework, and then sends records to different collectors. Traffic is matched based on the order in which classes are configured. After a match is found, no other classes are checked. The supported event types are flow-create, flow-denied, flow-teardown, and all. Records can be sent to different collectors. For example, with two collectors, you can do the following:

–Log all flow-denied events that match access-list 1 to collector 1.

–Log all flow-create events to collector 1.

–Log all flow-teardown events to collector 2.

•Delays the export of flow-create events.

Using NSEL and Syslog Messages

Table 73-1 lists the syslog messages that have an equivalent NSEL event, event ID, and extended event ID. The extended event ID provides more detail about the event (for example, which ACL—ingress or egress—has denied a flow).

Note Enabling NetFlow to export flow information makes the syslog messages that are listed in Table 73-1 redundant. In the interest of performance, we recommend that you disable redundant syslog messages, because the same information is exported through NetFlow.

Table 73-1 Syslog Messages and Equivalent NSEL Events

Syslog Message

Description

NSEL Event ID

NSEL Extended Event ID

106100

Generated whenever an ACL is encountered.

1—Flow was created (if the ACL allowed the flow).

3—Flow was denied (if the ACL denied the flow).

0—If the ACL allowed the flow.

1001—Flow was denied by the ingress ACL.

1002—Flow was denied by the egress ACL.

106015

A TCP flow was denied because the first packet was not a SYN packet.

3—Flow was denied.

1004—Flow was denied because the first packet was not a TCP SYN packet.

106023

When a flow was denied by an ACL attached to an interface through the access-group command.

3—Flow was denied.

1001—Flow was denied by the ingress ACL.

1002—Flow was denied by the egress ACL.

302013, 302015, 302017, 302020

TCP, UDP, GRE, and ICMP connection creation.

1—Flow was created.

0—Ignore.

302014, 302016, 302018, 302021

TCP, UDP, GRE, and ICMP connection teardown.

2—Flow was deleted.

0—Ignore.

> 2000—Flow was torn down.

313001

An ICMP packet to the device was denied.

3—Flow was denied.

1003—To-the-box flow was denied because of configuration.

313008

An ICMP v6 packet to the device was denied.

3—Flow was denied.

1003—To-the-box flow was denied because of configuration.

710003

An attempt to connect to the device interface was denied.

3—Flow was denied.

1003—To-the-box flow was denied because of configuration.

Note When NSEL and syslog messages are both enabled, there is no guarantee of chronological ordering between the two logging types.

Licensing Requirements for NSEL

The following table shows the licensing requirements for this feature:

Model

License Requirement

All models

Base License.

Prerequisites for NSEL

NSEL has the following prerequisites:

•IP address and hostname assignments must be unique throughout the NetFlow configuration.

•You must have at least one configured collector before you can use NSEL.

Guidelines and Limitations

This section includes the guidelines and limitations for this feature:

Context Mode Guidelines

Supported in single and multiple context modes.

Firewall Mode Guidelines

Supported in routed and transparent firewall modes.

IPv6 Guidelines

Supports IPv6 for the class-map, match access-list, and match any commands.

Additional Guidelines and Limitations

•If you previously configured flow-export actions using the flow-export enable command, and you upgrade to a later version, then your configuration will be automatically converted to the new Modular Policy Framework flow-export event-type command, described under the policy-map command. For more information, see the Release Notes for the Cisco ASA 5500 Series for Version 8.1(2).

•Flow-export actions are not supported in interface-based policies. You can configure flow-export actions in a class-map only with the match access-list, match any, or class-default commands. You can only apply flow-export actions in a global service policy.

Configuring NSEL

This section describes how to configure NSEL, and includes the following topics:

Using NetFlow

The NetFlow pane lets you enable the transmission of data about a flow of packets. To access this pane, choose Configuration > Device Management > Logging > NetFlow.

Note IP address and hostname assignments should be unique throughout the NetFlow configuration.

To use NetFlow, perform the following steps:

Step 1 Enter the template timeout rate, which is the interval (in minutes) at which template records are sent to all configured collectors. The default value is 30 minutes.

Step 2 To delay the export of flow-creation events and process a single flow-teardown event instead of a flow-creation event and a flow-teardown event, check the Delay export of flow creation events for short-lived flows check box, and then enter the number of seconds for the delay in the Delay By field.

Step 3 Specify the collector(s) to which NetFlow packets will be sent. You can configure a maximum of five collectors. To configure a collector, click Add to display the Add NetFlow Collector dialog box, and perform the following steps:

a. Choose the interface to which NetFlow packets will be sent from the drop-down list.

b. Enter the IP address or hostname and the UDP port number in the associated fields.

c. Click OK.

Step 4 To configure more collectors, repeat Step 2 for each additional collector.

Step 5 To change collector configuration details, select a collector and click Edit. To remove a configured collector, select it and click Delete.

Step 6 When NetFlow is enabled, certain syslog messages become redundant. To maintain system performance, we recommend that you disable all redundant syslog messages, because the same information is exported through NetFlow. To disable all redundant syslog messages, check the Disable redundant syslog messages check box. To display the redundant syslog messages and their status, click Show Redundant Syslog Messages.

The Redundant Syslog Messages dialog box appears. The Syslog ID field displays the redundant syslog message numbers. The Disabled field indicates whether or not the specified syslog message is disabled. Click OK to close this dialog box.

b. Click the Global - applies to all interfaces radio buttonto apply the rule to the global policy. Click Next.

c. Check the Source and Destination IP Address (uses ACL) check box or the Any traffic check box as traffic match criteria, or click the Use class-default as traffic class radio button. Click Next to continue to the Rule Actions screen.

Note NetFlow actions are available only for global service policy rules and are applicable only to the class-default traffic class and to traffic classes with traffic match criteria of "Source and Destination IP Address (uses ACL)" or "Any traffic."

Step 3 In the Rule Actions screen, click the NetFlow tab.

Step 4 To specify flow events, click Add to display the Add Flow Event dialog box, and then perform the following steps:

a. Choose the flow event type from the drop-down list. Available events are created, torn down, denied, or all.

b. Choose collectors to which you want events sent by checking the corresponding check boxes in the Send column.

c. To add, edit or delete collectors, or to configure other NetFlow settings (for example, syslog messages), click Manage to display the Manage NetFlow Collectors dialog box. Click OK to close the Manage NetFlow Collectors dialog box and return to the Add Flow Event dialog box. For more information about configuring collectors, see Step 3 of the "Using NetFlow" section.

Step 5 Click OK to close the Add Flow Event dialog box and return to the NetFlow tab.

Step 6 To change flow event entries, select an entry from the list, and click Edit. To remove flow event entries, select an entry from the list, and click Delete.

Step 7 Click Finish to exit the wizard.

Step 8 To edit a NetFlow service policy rule, perform the following steps:

Monitoring NSEL

You can use syslog messages to help troubleshoot errors or monitor system usage and performance.You can view real-time syslog messages that have been saved in the log buffer in a separate window, which include an explanation of the message, details about the message, and recommended actions to take, if necessary, to resolve an error. For more information, see the "Using NSEL and Syslog Messages" section.

Related Documents

Information about the implementation of NSEL on the adaptive security appliance

Cisco ASA 5500 Series Implementation Note for NetFlow Collectors

RFCs

RFC

Title

3954

Cisco Systems NetFlow Services Export Version 9

Feature History for NSEL

Table 73-2 lists each feature change and the platform release in which it was implemented. ASDM is backwards-compatible with multiple platform releases, so the specific ASDM release in which support was added is not listed.

Table 73-2 Feature History for NSEL

Feature Name

Platform Releases

Feature Information

NetFlow

8.1(1)

The NetFlow feature enhances the adaptive security appliance logging capabilities by logging flow-based events through the NetFlow protocol. NetFlow Version 9 services are used to export information about the progression of a flow from start to finish. The NetFlow implementation exports records that indicate significant events in the life of a flow. This implementation is different from traditional NetFlow, which exports data about flows at regular intervals. The NetFlow module also exports records about flows that are denied by access lists. You can configure an ASA 5580 to send the following events using NetFlow: flow create, flow teardown, and flow denied (only flows denied by ACLs are reported).

The following screen was introduced:

Configuration > Device Management > Logging > NetFlow.

NetFlow Filtering

8.1(2)

You can filter NetFlow events based on traffic and event-type, and then send records to different collectors. For example, you can log all flow-create events to one collector, and log flow-denied events to a different collector.

For short-lived flows, NetFlow collectors benefit from processing a single event instead of two events: flow create and flow teardown. You can configure a delay before sending the flow-create event. If the flow is torn down before the timer expires, only the flow teardown event is sent. The teardown event includes all information regarding the flow; no loss of information occurs.

The following screen was modified:

Configuration > Firewall > Service Policy Rules.

NSEL

8.2(1)

The NetFlow feature has been ported to all ASA 5500 series adaptive security appliances.